说明：  套接字（socket）是一个抽象层，应用程序可以通过它发送或接收数据，可对其进行像对文件一样的打开、读写和关闭等操作。套接字允许应用程序将I/O插入到网络中，并与网络中的其他应用程序进行通信。网络套接字是IP地址与端口的组合。
(Sockets are a layer of abstraction through which an application can send or receive data, which can be opened, read, written, and closed as if it were a file. Sockets allow applications to insert I/O into the network and communicate with other applications in the network. A network socket is a combination of IP addresses and ports.)